Undercut commutator



Oct. 18, 1966 T. J. BOYER 3,279,041

UNDERCUT COMMUTATOR Original Filed Dec. 20. 1962 2 Sheets-Sheet 2,

f1 zzgmf "\7-*2/ l l INVENTOR ffm/w45 ATTORNEYS if YER BY Mw?" the cuttoward the center of lthe commuator.

United States Patent O 3,279,041 UNDERCUT COMMUTATOR Thomas I. Boyer,Livonia, Mich., assignor to Ford Motor Company, Dearborn, Mich., acorporation of Delaware Original application Dec. 20, 1962, Ser. No.246,099, now

Patent No. 3,205,387, dated Sept. 7, 1965. Divided and this applicationMay 4, 1964, Ser. No. 364,743

5 Claims. (Cl. 29-155.54)

This application is a division of my copending application Ser. No.246,099, led December 20, 1962, now Patent 3,205,387, issued September7, 1965.

This invention relates to a method of undercutting the insulators of acommutator employed on dynamoelectric machines and to the commutatorproduced thereby.

In a dynamoelectric machine, it is desirable to use a narrow undercut atthe commutator insulator segments to preserve the maximum amount ofcommutator bar surface in contact with the brushes of the machine. Anarrow undercut is also effective in reducing the magnitude of -brushnoise. It is very difficult, however, to utilize a narrow undercut andstill remove all of the insulator segment `at the undercut. The reasonfor this difficulty is that commutator bars are usually not perfectlyformed, and as a result the commutator segments may `not Vbe properlypositioned angularly with the commutator. Also, the commutator bars andinsulator segments are often poorly indexed relative to one another,even in premium commutators. This means that the circumferentialdimension between 'the insulator segments may not be uniform. In massproduction techniques, therefore, it is diicult to employ machines thatutilize `a narrow undercut and will at the same time remove all of theinsulator segments at the undercuts. This results in poor commutation,poor performance, poor durability and poor brush life, and it alsoresults in brush noise.

The present invention is directed to a method of obviating theabove-mentioned difliculties and to the commutator formed thereby. Themethod of the invention entails undercutting the insulator `segment insuch as manner as to produce a dovetail slot. The slot is narrow at thecommutator surface and widens at the deepest portion of This providesthe benefit of a narrow slot at the surface of the commutator so thatthe commutator has low brush noise characteristics and has maximumcommutator bar surface in contact 4with the brushes -of thedynamoelectric machine. It ,also provides for `the wide cut necessary tofree the slot vof all the insulating material.

The dovetail slot may be achieved by -means of a 4circular millingcutter that is inclined at a slight angle with respect to the insulatorsegment. A lirsticut is then taken along the length of the insulatorsegment. A circular milling cutter is then inclined at a similar anglein the opposite direction with respect to 'the insulator segrnent and `a'secondcut is taken. 'This produces a `dovetail slot at each insulatorsegment.

'In the preferred manner of performing the method of the invention, `thedovetail slots may be formed by the use of two circular milling cuttersthat are mounted on a common shaft or arbor. One circular milling cutterwill make all of the cuts at the insulator segments inclined in onedirection and the other circular milling cutter will make all ofthe cutsinclined in the'opposite direction. After the two circular fmillingcutters have 'made a pair of Acuts into a set of insulator segments, thecommutator is rotated about its axis to bring the next set of insulatorsegments into proper cutting relationship with these circular millingcutters. Mounting the two circular milling cutters on a common lshaftwill assist greatly in holding the exact location of the second cut at'sulator segment 12.

3,279,041. Patented Oct. 18, 19,65

"ice

each of the insulator .segments relative to the rst cut at each of theinsulator segments.

An object of the invention is the provision of Ia method forundercutting the vinsulator segments on commutators that will remove allof the insulator at the undercut area and that will leave `a maximumamount of commutator bar surface in contact with the brushes -of thedynamoelectric machine.

Another object of the invention is to provide a method for undercuttingthe insulator segments of commutators that forms an undercut slot in acommutator at each insulator segment that is narrow .at the surface ofthe commutator and that is wide at the portion of the slot positionednearest the center of the commutator.

A further object of the invention is the provision yof a commutator thatprovides a maximum amount of commutator bar surface in .contact with thebrushes of a dynamoelectric machine and that simultaneously has all ofthe insulating material `of `the insulator .segments removed in the`area of the undercut slots of the insulator segments.

Other objects and attendant advantages of the invention will become moreapparent as the specification is considered in connection with theattached drawings in which:

FIGURE i is a perspective view of the .commutator of the presentinvention;

FIGURE 2 is an enlarged sectional view of a portion of the commutatorprior to Aundercut'ting showing adjacent conductive bars or segmentsseparated by an insulator segment;

FIGURE 3 is a view similar to FIGURE 2 and l,showing how the commutatoris undercut, and

FIGURE 4 is a partial schematic view of a means for carrying out themethods of the invention.

Referring now to FIGURE l, there is shown the cornmutator 10 of thepresent invention that is formed of a plurality of commutator bars orconductive segments 11 that are separated by a plurality of insulatorsegments 12. As conventional incommutator structures, the conductivesegments 11 are formed of copper bars while the insulator segments 12are formed of Ia mica base insulating material. The commutator is formedso that the alternating conductive bars -or segments 11 and insulatorsegments 12 form a cylindrical array in which the insulator segments 12extend radially inwardly from the surface V13 of the commutator towardthe center of the cylindrical array. The commutator 10 is undercut ateach of the insulator segments 12 to form a dovetail slot 14 thatextends, through the length of the commutator that is adapted to contactan electrical contact brush. This dovetail slot is narrow at the surfacev13 vof the commutator and -is wider at the bottom thereof `toward thecenter of the commutator 10. This type of `slot or undercut has theadvantages pointed out in the introductory portion of the specification.It `provides a maximum amount of commutator segments or bars in contact-with the electrical`brushes of (the dynamoelectric machine and itinsures that all ofthe insulating material is removed in the area -ofthe undercut.

Referring now to FIGURES 2 iand V3, the method of undercutting theinsulator segments i the commutator 10 and forming the dovetail slots 14will nowbe described. The method comprises making a :first cut Vinto thecommutatorat the insulator :segment 13 that is inclined in one`directionewithrrespect to the insulator segment. This rst cut -isdirected into `theconductive `segment 11 positioned on one side of the-insnlator segment. A second cut is then made at the insulatorsegmenti12 in a direction that is inclined to the insulator segment in adirection opposite to the first cut. This ysecondcutfisdirected into theconductive segment 1-1 positionedon the other side of the in- It can beappreciated that these two cuts form the dovetail slot 14 at theinsulator segment and that the narrow portion of the dovetail slot atthe surface 13 of the commutator spans or is wider than the mica segmentat this position. Although the method is not so limited, it is preferredthat the two inclined cuts be made of the same width (wider than theinsulator segment 12) and be in the same position on the surface 13 ofthe commutator as shown in FIGURES 2 and 3. Itis to be understood thatthe first and second cuts described above extend through the length ofthe commutator that may come into contact with the electrical brushes ofthe dynamoelectric machine.

A practical means for making the dovetail slots 14 in the commutator 10and for carrying out the method of the invention is shown in FIGURE 4. Afirst circular milling cutter 21 and a second circular milling cutter 22are mounted on a common rotatable shaft 23. This shaft is adapted formovement downwardly, as shown in FIG- URE 4, to make the first andsecond cuts described above and for movement in a directionperpendicular to the plane of the drawings so that the cuts are madethrough a desired length of the commutator. The circular milling cutter21 makes-the rst cut, as described above, and the circular millingcutter 22 makes the second cut, as described above, since the circularmilling cutter 22 is inclined at an angle with respect to the conductivesegments undergoing cutting opposite to the angle of the circularmilling cutter 21. In practice, the commutator assembly is rotatedthrough one conductive segment 11 after the circular milling cutters A21and 22 each makes a cut. It can be seen that the dovetail slot 14 willbe completed at each of the insulator segments 12 when the circularmilling cutter 21 has made a first cut at each of the insulator segments12 and the second circular milling cutter 22 has made a second cut ateach of the insulator segments 12.`

It can be readily appreciated by an inspection of FIG- URE 4 that thecircular milling cutters 21 and 22 are rotatable about an axis that issubstantially normal to the direction of the radially extendinginsulator segment 12A that is positioned between the circular millingcutters 21 and 22 and the insulator segments 12B and 12C that are beingcut by these cutters.

Considered in a broader aspect, it can be appreciated that the first cutat an insulator segment 12 is made by a circular milling cutter that isrotatable about an axis that is substantially normal to the adjacentinsulator segment positioned on one side of the insulator segmentundergoing cutting. The second cut is made by a milling cutter that isrotatable about an axis that is substantially normal to the adjacentinsulator segment positioned on the other side of the insulator segmentundergoing cutting. This can be appreciated by an inspection of FIGURE 4and by consideringthat the commutator 10 is rotated or indexed in acounterclockwise direction.

As viewed in FIGURE 4, the insulator segment 12C is being cut by thecircular milling cutter 22. The circular milling cutter 22 is rotatableabout an axis that is substantially normal to the insulator segment 12Apositioned to the left of the insulator segment 12C. After this cuttingoperation is performed, the second cut in the insulatorV segment 12Cwill be made by the circular milling cutter 21 after the commutatorassembly has been rotated or indexed counterclockwise to bring theinsulator segment 12C under the circular milling cutter 21. In thisposition, the circular milling cutter 21 is rotatable about an axis thatis substantially normal to the insulator segment 12D that is nowpositioned between the circular milling cutters 21 and 22. The insulatorsegment 12D is the insulator segment adjacent the insulator segment 12Cand positioned on the other side thereof from the insulator segment 12A.From this description of the methodof cutting the dovetail slots 14 atthe insulator segments 12 of the commutator 10 to undercut thecommutator, it can be seen that the commutator assembly may remainstationary and that both circular milling cutters 21 and 22 may berevolved about the commutator assembly 10 to make the cuts in thedirections described above. It can also be appreciated that a singlemilling cutter could be employed to cut the dovetail slots.

The advantage of using two circular milling cutters on a common shaft isthat this assembly will assist greatly in holding the exact location ofthe second cut1relative to the first cut.

The present invention thus provides a method for undercutting theinsulator segments of a commutator in which the undercut is narrow atthe surface to preserve the maximum amount of conductive bars orsegments in contact' with the brushes and is wider as the undercutdeepens to` insure that .all the insulator in the area of the undercutis removed.

It will be understood that the invention is not to be limited to theexact construction shown and described,`

but that various changes and modifications may be made without departingfrom the spirit and scope of the inven-` tion as defined in the appendedclaims.

I claim:

1. A method of undercutting a commutator for a dynamo-electric machinethat includes a first and a second conductive segment separated by aninsulator segment comprising, making a first cut into said commutator atsaid insulator, said first cut spanning said insulator seg-` ment at thesurface of said insulator and being directed at an angle to saidinsulator and into said first conductive segment, and making a secondcut into said commutator at the same position on the surface of saidcommutator as said first cut, said second cut y'being directed atanangle! to said insulator and into said second conductive segment. 2. Amethod of undercutting a commutator for a` spanning the insulatorsegments atthe surface of said` commutator, and being inclined to saidinsulator segments toward a conductive segment positioned on one side ofeach lnsulator segment, making second cuts into said com-` mutator ateach of said insulator segments and at the same position on the surfaceof said commutator at each in- -sulator segment as said first cuts, saidsecond cuts being 1 inclined toward a conductive segment positioned onthe other side of each insulator segment.

3. A method of undercutting a commutator for a dynamo-electric machinethat includes a pair of conductive segments separated by an insulatorsegment comprising, making a first cut into said insulator segment ofsaid commutator at an angle to said insulator and making:

a second cut into said insulator segment at an angle to form a dovetailslot in said commutator at said insulat tor segment that spans saidinsulator segment at the surt face of said commutator.

4. A method of undercutting a commutator for a dynamo-electn'c machinethat includes a cylindrical array of conductive commutator segmentsseparated by insulator segments that are directed radially inwardly fromthe sur. face of said commutator toward the center of said cylin` tmaking a first cut into a pair of: spaced insulator segments that areseparated Iby an n`` termediate pair of conductive segments and aninsulator drical array comprising,

segment by a pair of milling cutters rotating about an axis that issubstantially normal to the direction of said intermediate insulatorsegment, rotating said commutator about its cylindrical axis and makinga second cut into` each of said spaced insulator segments by the millingcut-` ter that made the first cut in the other of the spaced in-`sulator segments.

5. A method of undercutting a commutator for a dynamo-electric machinethat includes a cylindrical array of conductive commutator segmentsseparated by insulator segments that are directed radially inwardly fromthe surface of ysaid commutator toward the center of ysaid cylindricalarray comprising, making a first cut into said commutator at one of saidinsulator segments of a Width greater than said insulator segment by amilling cutter that is rotatable about an axis substantially normal tothe adjacent insulator segment positioned on one side of said oneinsulator segment, and making a second cut into said commutator at saidone insulator segment of approximately the same width las said rst cutby a milling cutter that is rotatable about an axis that issubstantially normal to the adjacent insulator segment positioned on theother side of said one insulator segment.

References Cited bythe Examiner UNITED STATES PATENTS 1,614,558 1/1927Kasle'y 90-11 3,010,182 11/1961 Quinlan 29-155.54 `3,066,387 12/ 1962Herbst 29-155.54

10 JOHN F. CAMPBELL, Primary Examiner.

J. M. ROMANCHIK, Assistant Examiner.

1. A METHOD OF UNDERCUTTING A COMMUTATOR FOR A DYNAMO-ELECTRIC MACHINETHAT INCLUDES A FIRST AND A SECOND CONDUCTIVE SEGMENT SEPARATED BY ANINSULATOR SEGMENT COMPRISING, MAKING A FIRST CUT INTO SAID COMMUTATOR ATSAID INSULATOR, SAID FIRST CUT SPANNING SAID INSULATOR SEGMENT AT THESURFACE OF SAID INSULATOR AND BEING DIRECTED